why you should install a higher pressure fpr

[mbtoloczko]

I've been looking doing a bit of research on the fuel delivery rate of our SVXes. Based on what I've found, it looks like the stock fuel system can handle no more than 230 HP without going lean at WOT. The stock injectors are 275 cc/min capacity (at 43 psi), and according to the service manual, the SVX fuel pressure is set to 36 psi at WOT. If I have a jaunt over to this page:

http://www.rceng.com/technical.htm

and in the first worksheet use 230 HP, 6 injectors, a BSFC of 0.5, a duty cycle of 0.8, and a max fuel pressure of 36 PSI, then the worksheet spits out that 277 cc/min fuel injectors are needed for these conditions. That means that any aftermarket mods which improve airflow are going to be pushing the fuel delivery system beyond its limits. This would explain why svxfiles has been seeing improvements in power when he installed a 2000 Legacy 2.5 fuel pressure regulator which is good for 43 psi in his mildly modified SVX. Food for thought folks.

[Trevor]

Worthwhile thoughts and info for sure.

But --- how do I REDUCE the gas my car uses when my wife hacks it about in city traffic etc ? The SVX has proven to be a hungry animal. Even so, it is quite a family pet.

[mbtoloczko]

At less than WOT, the ECU shortens the fuel pulse length to compensate for the higher fuel pressure.

[AFBeefcake]

so if you do any mods you should up the fuel to 43 PSI?

where can i get one and how much?

[Trevor]

Originally posted by mbtoloczko
At less than WOT, the ECU shortens the fuel pulse length to compensate for the higher fuel pressure.

Yes, I am aware of how the ECU functions. I was referring to the hope of improving fuel consumption in respect of an existing car in standard condition, accepting the obvious of having everything in good condition.

Indications are that many desire such improvement. Posting the obvious -- " Keep your foot off the gas ", will earn a booby prize.

[mbtoloczko]

Originally posted by Trevor


Yes, I am aware of how the ECU functions. I was referring to the hope of improving fuel consumption in respect of an existing car in standard condition, accepting the obvious of having everything in good condition.

Indications are that many desire such improvement. Posting the obvious -- " Keep your foot off the gas ", will earn a booby prize.

Ah. I was too focused on the topic. Yeah, its amazing that the car is such a gas guzzler considering that the ECU keeps the a/f mixture right on stoich.

[mbtoloczko]

Originally posted by AFBeefcake
so if you do any mods you should up the fuel to 43 PSI?

where can i get one and how much?

svxfiles said that a fuel pressure regulator from a 2000 Legacy 2.5 is rated at around 45 psi and is a bolt-in replacement. I called up a service shop today to get some info, and indeed that regulator is set to 43 psi. The price is about $70 online. I haven't seen one yet though, so I don't know if its a bolt-in replacement.

[Trevor]

Originally posted by mbtoloczko


Ah. I was too focused on the topic. Yeah, its amazing that the car is such a gas guzzler considering that the ECU keeps the a/f mixture right on stoich.

What puzzles me is that one can doodle about town without exceeding 2200 RPM and the thing still guzzles ! Maybe the AC requires mega HP.

[immortal_suby]

If that is a bolt in replacement then why do the guys putting turbos in the 2.5RS use an svx FPR? It would seem the legacy unit would be better.

And if this does pan out, don't throw out your old svx fpr - they are very easy to sell -even used- on the impreza forums.


<---- heading over to nasioc tech forums

[AFBeefcake]

any one have a part number for the 2.5 FPR?

[SVXRide]

Mychailo,
Does this mean you're going to be the test mule for this mod? I'm in the middle of drawing up a new air box to allow for a larger drop in filter (stupid ABS keeps getting in the way ) so allowing for more fuel flow to go with increased air flow works for me!
-Bill (definitely "keeping his foot off the gas" )

[Phast SVX]

Originally posted by mbtoloczko


Ah. I was too focused on the topic. Yeah, its amazing that the car is such a gas guzzler considering that the ECU keeps the a/f mixture right on stoich.

our car dosnt run stoick, it runs slightly rich, as every car does for safety.

[AFBeefcake]

would some thing like this work

http://cgi.ebay.com/ebaymotors/ws/eB...tem=2433517641

they say they have Fuel Rail Adapters for Subaru

[Chicane]

Originally posted by Phast SVX

our car dosnt run stoick, it runs slightly rich, as every car does for safety.

I would say it runs richer than most cars. :| I don't have any evidence for this other than how badly it sucks gas when you're not doing anything. I think in the upper RPMs, it leans out a little, and you're engine is being a lot more efficient. That's just my guess though. I can just sense it with my ESVXP.

- Rob

[AFBeefcake]

or would it be better to go to a juck yard and just buy one off a 2000 2.5 legacy